[html-formfu] set non-db column and use in ->update

[Carl Franks]

> I'd like to set a non db column value eg;
>
> __PACKAGE__->mk_group_accessors('simple' => qw/filter_update/);
>
> $row->filter_update(1);

Hi Stephen,
Sorry I've not managed to look at your earlier performance issues yet
- I've not had any free time available :(